Method for controlling the volume of a molecular beam

ABSTRACT

A molecular beam source for use in thin-film accumulation, which enables the adjustment of the volume of a molecular beam, which is discharged per hour by using a needle valve, to be constant irrespective of a decrease in a thin-film element-forming material remaining within a crucible, contains heaters  32  and  42  for heating the thin-film element-forming materials “a” and “b” within crucibles  31  and  41 , and valves  33  and  43  for adjusting the volumes to be discharged of molecules of the thin-film element forming materials “a” and “b”, which are generated within the crucibles  31  and  41 . It further contains a controller for adjusting the opening of the valves  33  and  43  by servomotors  36  and  46  through feeding back information relating to the volumes of the molecular beams, which are obtained from film-thickness meters  16  and  26  for detecting the volume of molecular beams discharged towards the film-forming surface, a heating electric power source for supplying an electric power to heaters  32  and  42 , and a controller for adjusting the electric power to be supplied to the heating electric power source depending upon the information relating to the volume of the molecular sources and information relating to the opening of the valves.

BACKGROUND OF THE INVENTION

The present invention relates to a molecular beam source used forthin-film accumulation or deposition and a method for controlling theamount or volume of a molecular beam, through heating a material to beformed on a film-forming surface of a solid body or matter, such as, asubstrate, etc., in the form of a thin-film, by melting, sublimating orevaporating material(s) for forming a thin-film element, i.e.,generating evaporated molecules for growing the thin-film(s) upon thesurface of the solid body, and it relates, in particular, to a molecularbeam source for use in thin-film accumulation, and is suitable foraccumulating or depositing an organic thin-film upon a film-formingsurface of the solid body, such as, the substrate, etc., continuouslyfor a long time, and a method for controlling an amount or volume of themolecular beam therefrom.

A thin-film deposition apparatus, called a “molecular beam epitaxyapparatus”, comprises a decompressable vacuum chamber, into which asubstrate, such as a semiconductor wafer, etc., can be mounted under ahigh vacuum condition, and heated up to a desired temperature, whileproviding a molecule supply source cell, such as a Knudsen cell, etc.,for example, opposing the film-forming surface thereof. Thus, a materialfor forming a thin-film element (hereinafter, a thin-filmelement-forming material), which is put into within a crucible of themolecule supply source cell, is heated by means of a heater, to besublimated, melted or evaporated, so that a molecular beam generatedthereby is incident upon the film-forming surface of the substrate,i.e., bringing about the epitaxial growth of the molecules of thethin-film element-forming material on the film-forming surface, therebyforming a film of the thin-film element-forming material.

Such a molecular beam source cell, to be applied in a thin-filmdeposition or accumulation apparatus, has a crucible made of a materialsuch as PBN (Pyrolithic Boron Nitride), etc., for example, and is highlystable, thermally as well as chemically, so as to receive the thin-filmelement-forming material therein, and an electric heater is providedsurrounding the outside of the crucible to heat the thin-filmelement-forming material therein, i.e., generating the molecules thereofthrough sublimation, melting or evaporation of the thin-filmelement-forming material.

In recent years, attention has been paid to an organic thin-filmelement, such as, an organic electroluminescence (EL) and/or an organicsemiconductor, for example, representatively. Those thin-film elementscan be obtained, i.e., the thin-film element-forming material is heatedwithin the vacuum, so as to blast the vapor thereof upon the surface ofthe substrate, and then it is cooled down to be solidified and bondedthereon. In general, the following method is applied, i.e., thethin-film element-forming material is put into the crucible, which ismade of an inorganic material such as PBN, etc., or a material having ahigh melting-point, such as tungsten, etc., and then the material to beformed as a film is heated by the heater provided around the crucible,thereby generating the vapor thereof to be blasted onto the substrate.

An organic electroluminescence (EL) material, being a representativeexample of an organic thin-film element, is an element for forming aluminous layer from an organic low-molecular material or an organichigh-molecular material, which has EL luminous ability, and attention ispaid to, in particular, the characteristics thereof, i.e., as an elementof the self-luminous type. In the basic structures thereof, for example,on a film of a hole transportation material, such as triphenyl diamine(TPD) or the like, formed on a hole injection electrode, is laminated ordeposited a fluorescent material such as aluminum-quinolinol complex(Alq₃), etc., as the luminous layer and, further thereon is formed anelectrode of a metal having a small work function, such as Mg, Li, orCs, etc., as an electron-injection electrode. However, the materials ofthe thin-film elements are expensive, in general.

By the way, when building up the thin-film elements, there is also thenecessity of the time for exchanging the substrates, on the surfaces ofwhich the thin film should be formed, and for adjusting the position ofa mask for blasting the material only onto necessary portions thereof,etc. However, since many of the materials for the organic thin-filmelement as was mentioned above is sublimated or evaporated at relativelylow temperatures, the material is evaporated, even during the time ofexchanging the substrates and/or aligning the position of the mask,etc., i.e., there is a drawback that the very expensive material iswasted, uselessly.

Then, as is described in the following Patent Document 1, which will bementioned below, there is proposed a molecule supply source for use inthin-film deposition of receiving the crucibles therein, each of whichis hermetically sealed or closed in the structure, wherein a moleculedischarge passage is provided for directing the molecules of thethin-film element material, which are generated within the crucibles,towards the film-forming surface, and further comprising a needle valvefor adjusting an amount or volume of molecular supply on the way of themolecule discharge passage.

With the molecule supply source for use in thin-film depositioncomprising such the valve mechanism, it is possible to cut or shut offthe discharge of the vapor of the material for the thin-film element,which is generated within the crucible, by means of the valve, and inaddition thereto, to adjust the amount or volume of the molecular supplyby means of the needle valve, as well. For the purpose of forming thethin-film while maintaining a constant film-thickness and qualitythereof, it is effective to keep the volume of the molecular supplyconstant per hour, which is discharged from the molecular supply source.

As a representative material for the organic thin-film elementsmentioned above, there is already known a material of the EL thin-filmelement, and many of these materials for forming thin-film elements aregranulated or powdered, and they are put into the crucibles in thatcondition. Thus, with the heating of it within the crucible by means ofthe heater, which is provided outside the crucible, the material of theEL thin-film element is heated and sublimated, and is evaporated to bedischarged towards the substrate, and thereby deposited on thefilm-forming surface of the substrate for forming a film thereon.

When the material of the EL thin-film element is sublimated andevaporated within the crucible to be discharged therefrom, the volume isreduced, gradually, of the material of the EL thin-film elementremaining within the crucible. Then, since the surface area thereof isalso reduced within the crucible, the volume of the sublimation of thematerial of the EL thin-film element is also reduced, gradually, withinthe crucible. Accordingly, for the purpose of maintaining the volume ofthe molecular supply discharged from the molecular supply source for usein the deposition of the thin-films, it is necessary to make a largeropening of the needle valve, i.e., the ratio of the cross-section of theflow passage to that when the valve is fully opened, thereby to maintainthe volume of the molecular supply discharged from the molecular supplysource for use in the deposition of thin-films.

However, with the adjustment made in the volume of the molecular supplyby means of the needle valve, it is finite or has a limit, i.e., whenthe needle valve is opened fully, then it is impossible to increase thevolume of the molecular supply much more than that.

In the Patent Document 2 mentioned below, there are disclosed two (2)controller means, as the adjustment means for adjusting the volume ofthe molecular supply. One of them is an adjustment means for adjustingthe volume of the molecular supply by means of the valve, as wasmentioned above. The other one is a controller means depending on thetemperature at which the crucible is heated up by means of the heater.However, the latter controller means, depending on the temperature atwhich the crucible is heated up by means of the heater, is not suitablefor adjusting the volume of the molecular supply with any accuracybecause the control of the controller is direct and has a time delay.

(Patent Document 1) Japanese Patent Laying-Open No. 2003-95787 (2003);and

(Patent Document 2) Japanese Patent Laying-Open No. Hei 6-80496 (1994).

BRIEF SUMMARY OF THE INVENTION

According to the present invention, which is accomplished by taking thedrawbacks of the conventional molecule supply source for use inthin-film deposition and the method for controlling the molecule supplythereof into consideration, an object thereof is to provide a moleculesupply source for use in thin-film deposition and also a method forcontrolling the amount of molecule supply, for enabling the adjustmentof the volume of the molecule supply to be constant per hour by means ofthe needle valve, irrespective of a decrease in the remaining volume ofthe material for forming the thin-film elements within the cruciblethrough the discharge of molecules from the molecule supply source foruse in thin-film deposition.

Thus, according to the present invention, there is provided a moleculebeam source for use in accumulating a thin-film and evaporating amaterial of a thin-film element, comprising: a crucible for heating thematerial of the thin-film element; a heater for heating said crucible; amolecule discharge passage for discharging molecules of the material ofthe thin-film element generated within said crucible towards afilm-forming surface; a vacuum container having a hermetically sealedstructure for receiving said crucible, said heater and said moleculedischarge passage therein; a valve for adjusting the volume of themolecular beam discharged, positioned at said molecule dischargepassage; a detection means for detecting the volume of the molecularbeam discharged towards said film-forming surface; a controller meansfor adjusting the opening of a valve by a valve driving means throughfeed-back information relating to the volume of the molecular beamdetected by said detection means; a heating electric power source forsupplying electric power for use in heating said heater; and a controlmeans for adjusting the electric power to be supplied to said heatingelectric power source depending on said information relating to thevolume of the molecular beam and valve opening information.

Also, according to the present invention, there is provided a method forcontrolling the volume of a molecular beam within a molecule beam sourceused in accumulating a thin-film by evaporating a material of thethin-film element, comprising the following steps of: adjusting theelectric power to the electric power source for heating said crucible ifthe valve opening necessary for obtaining a predetermined volume of themolecular beam is equal to a predetermined reference value or largerthan that, when evaporating an organic material upon a substrate,continuously, and thereby controlling the valve opening to fall within arange.

With the molecule beam source for use of accumulating the thin-film andthe method for controlling the volume of the molecular beam with the usethereof, according to the present invention, as was mentioned above,while basing the control through the control means of the volume of themolecular beam, by means of the valve enabling accurate control of thevolume of the molecular beam to be discharged, the volume of evaporationwithin the crucible per hour is maintained by increasing the temperatureof the heater, when the material remaining within the crucible isconsumed and becomes smaller in the volume thereof, thereby enabling themaintaining of the discharge volume of the molecular beam at a constantlevel. With this, even when consuming the material of the thin-filmelement within the crucible, i.e., the volume of the same is decreasedgradually, it is possible to maintain the amount of the volume of themolecular beam to be discharged as desired, within a controllable rangewith the use of the valve. Thus, up to the time when the remainder ofthe material of the thin-film element within the crucible comes down tobe very small, it is always possible to maintain the volume of themolecular beam discharged at a constant value. Also, as was mentionedabove, with the control of the volume of the molecular beam through theadjustment of the heater temperature, it is impossible to obtain anaccurate control due to the time delay, etc. However, applying this incombination with the adjustment of the opening of the valve, it ispossible to obtain the accurate control of the volume of the molecularbeam.

As was explained above, according to the present invention, with themolecule beam source for use in accumulating the thin-film and themethod for controlling the volume of a molecular beam with the usethereof, as was mentioned above, it is possible to achieve the controlof maintaining the volume of the molecular beam discharged at a constantvalue up to the end, even if the material remaining within the crucibleis consumed and thereby becomes small in the volume thereof, gradually.Furthermore, by applying the adjustment of the opening of the valve incombination with the adjustments of the needle valve and the heatertemperature, it is possible to control the volume of the molecular beam,accurately.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF DRAWINGS

Those and other objects, features and advantages of the presentinvention will become more readily apparent from the following detaileddescription when taken in conjunction with the accompanying drawings,wherein:

FIG. 1 is a vertical cross-section view showing an attachment portion ofa vacuum chamber, having two (2) molecular beam source cells attachedthereon, for using them at the same time, according to an embodiment ofthe present invention;

FIG. 2 is a vertical cross-section view showing one of the molecularbeam source cells, according to the same embodiment mentioned above;

FIG. 3 is also a vertical cross-section view for showing the othermolecular beam source cell, according to the same embodiment mentionedabove;

FIGS. 4( a) and 4(b) are enlarged cross-section views for showing an “A”portion and a “B” portion in FIGS. 2 and 3, respectively;

FIG. 5 is a block diagram for showing an example of controls for valvesof the molecular beam source cells and an electric power source of aheater, according to the embodiment mentioned above; and

FIG. 6 is a time diagram for showing an example of the controls for thevalves of the molecular beam source cells and the electric power sourceof the heater, according to the embodiment mentioned above.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, the molecular beam source for use inthin-film deposition or accumulation is built with molecular beam sourcecells, each having a valve provided between a crucible and a vacuumchamber, a detector provided within the vacuum chamber for detecting anamount or volume of molecular beams discharged, a valve-driving meansfor controlling the needle valves of the molecular beam source cells onthe basis of a signal from that detector, and a circuit for controllingthe electric power for heating the crucible on the basis of a valveposition signal.

Hereinafter, embodiments according to the present invention will befully explained by referring to the attached drawings.

FIG. 1 shows an example of a complex molecular beam source cell,combining a first molecular beam source cell 1 for evaporating a maincomponent, i.e. a thin-film element-forming material “a”, such as amaterial for forming a thin-film on a substrate 51, and a secondmolecular beam source cell 2 for evaporating a sub-component, i.e., athin-film element-forming material “b”, such as a dopant, etc.

Each of those molecular beam source cells 1 and 2 comprises amaterial-receiving portion 3 or 4, having a crucible 31 or 41 forreceiving the thin-film element-forming material “a” or “b” therein anda heater 32 or 42 for sublimating or evaporating the thin-filmelement-forming material “a” or “b”, a valve 33 or 43 to beopened/closed, so as to leak or stop the molecules of the thin-filmelement-forming material “a” or “b”, which is discharged from thematerial-receiving portion 3 or 4, and a molecule radiation portion 11or 21, for discharging the molecular beam of the thin-filmelement-forming material “a” or “b” transmitted through the valve 33 or43, towards the substrate 51, through re-heating it by means of a heater15 or 24. This molecule radiation portion 11 or 21 is enclosed by ashroud 40, which is cooled with liquid nitrogen, etc. However, thoughnot shown in the figure, the temperatures of the crucibles are measuredby a temperature measurement means, respectively, such as, athermocouple or the like, for example, a measuring point of which isprovided at a bottom portion thereof.

On the side of a substrate 51 having a film-forming surface to bedeposited with a thin film thereof, upon receipt of the molecular beamsof the thin-film element-forming materials “a” and “b”, which aredischarged from those molecular beam source cells 1 and 2, there areprovided film-thickness meters 16 and 26, respectively, for detectingthe volume of the molecular beams, which are discharged towards thatfilm-forming surface. The film-thickness meter 16 is a detection meansfor detecting the volume of the molecular beam of the thin-filmelement-forming material “a” discharged from the molecular beam sourcecell 1, while the film-thickness meter 26 is a detection means fordetecting the volume of the molecular beam of the thin-filmelement-forming material “b” discharged from the molecular beam sourcecell 2.

The molecules of the thin-film element-forming materials “a” and “b”,being discharged from molecule discharge openings 14 and 24 of themolecular beam cells 1 and 2, are directed onto the substrate 51, whichis positioned opposite thereto, to be evaporated thereon. In thisinstance, a portion of each of the materials is directed towards thefilm-thickness meter 16 or 26, and then the volume can be detected ofthe molecular beam of the thin-film element-forming material “a” or “b”,which is captured by the film-thickness meter 16 or 26. Since there is acertain relationship between the volume of the molecular beam detectedand the volume of material depositing onto the substrate, the volume ofthe thin-film element-forming material “a” or “b” can be determined,which is deposited on the substrate.

FIG. 2 shows the first molecular beam source cell 1, which sublimates orevaporates the main component, i.e., the thin-film element-formingmaterial “a”, thereby irradiating it. The material-receiving portion 3of this molecular beam source cell 1 has the cylindrical container-likecrucible 31, which is made of a high heat conduction material of ametal, such as, SUS, etc., and within the crucible 31 is put thethin-film element-forming material “a”.

Surrounding the crucible 31 is provided the heater 32 and, further, ashroud 39 is provided surrounding an outside thereof, which is cooledthrough liquid nitrogen, etc. A heat value of the heater 32 iscontrolled through the temperature measuring means (not shown in thefigure), such as, the thermocouple or the like, which is provided on thecrucible 31, and the thin-film element-forming material “a” is heatedwithin the crucible 31, therefore, the thin-film element-formingmaterial “a” is sublimated or evaporated within the crucible 31, therebygenerating the molecules thereof. Also, by stopping the heat-generationof the heater 32 while cooling an inside of the crucible 31 with the aidof the shroud 39, the thin-film element-forming material “a” is cooleddown, thereby stopping the sublimation or evaporation of the thin-filmelement-forming material.

On the side of the crucible 31, from which the molecules of thethin-film element-forming material are discharged, is provided the valve33. This valve 33 is a so-called needle valve having a sharp needle 34and a valve seat 35 for forming a molecule passage opening, which isclosed (or shut off) in the flow passage thereof or narrowed in thecross-section area thereof through insertion of a tip of the needle 34.The needle 34 mentioned above is moved in the direction of a centralaxis thereof, with the aid of a linear movement that is introducedthrough a bellows 37 from a servomotor 36, which is provided as anactuator.

FIG. 4( a) is an enlarged view of the “A” portion shown in FIG. 2,wherein the tip of the needle 34 is inserted into the molecule passageopening 38 of the valve sheet 35 through the linear movement thereofmentioned above, or it is separated from the molecule passage opening38, thereby to open the molecule passage opening 38. This FIG. 4( a)shows the condition where the tip of the needle 34 is inserted into themolecule passage opening 38 of the valve seat 35, so as to block themolecule passage opening 38, i.e., the condition where the valve 33 isclosed or shut off.

As is shown in FIG. 2, at the end of a direction passing through themolecule passage opening of the valve seat 35, which can beopened/closed by means of the valve 33, there is provided the moleculeradiation portion 11. This molecule radiation portion 11 has acylinder-like molecule heater chamber 12, and surrounding this moleculeheater chamber 12 is provided the heater 15. Molecules of the thin-filmelement-forming material, leaking from the side of the valve 33mentioned above and reaching the molecule radiation portion 11 areheated again (i.e., re-heated), up to the desired temperature withinthis molecule heater chamber 12, and are irradiated from the moleculedischarge opening 14 towards the substrate.

On the other hand, FIG. 3 shows the second molecular beam source cell 2,which sublimates or evaporates the sub-component, i.e., the thin-filmelement-forming material “b”, thereby irradiating it. The structures ofthis second molecular beam source cell 2 are basically the same as thatof the first molecular beam source cell 1 mentioned above.

Thus, the material-receiving portion 4 of this molecular beam sourcecell 2 has the cylindrical container-like crucible 41, which is alsomade of the high heat conduction material of a metal, such as, SUS,etc., and within the crucible 41 is put the thin-film element-formingmaterial “b”.

Surrounding the crucible 41 is provided the heater 42, and further ashroud 49 is provided surrounding an outside thereof, which is cooledthrough the liquid nitrogen, etc. The structures and functions of theheater 42 and the shroud 49 are completely the same as those of theheater 32 and the shroud 39, which are mentioned by referring to FIG. 2.

On the side of the crucible 41, from which the molecules of thethin-film element-forming material are discharged, is provided the valve43. This valve 43 is also a so-called needle valve, having a sharpneedle 44 and a valve seat 45 for forming a molecule passage opening,which is closed (or shut off) in the flow passage thereof or narrowed inthe cross-section area thereof through the insertion of a tip of theneedle 44. The needle 44 mentioned above is moved in the direction of acentral axis thereof with the aid of a linear movement that isintroduced through a bellows 47 from a servomotor 46, which is providedas an actuator.

FIG. 4( b) is an enlarged view of the “B” portion shown in FIG. 3,wherein the tip of the needle 44 is inserted into the molecule passageopening 48 of the valve seat 45 through the linear movement thereofmentioned above, or it is separated from the molecule passage opening 48to thereby open the molecule passage opening 48. This molecular beamsource cell 2 is provided for discharging the sub-component or material,such as the dopant, etc. and, for this reason, it is designed such thatan opening diameter of the valve seat 45 and a taper-angle at the tip ofthe needle and the maximum opening area of the valve 43, as well, aresmaller than those of the molecular beam source cell mentioned above fordischarging the main component or material. Thus, it is possible toaccurately control the volume of the molecular beam.

As is shown in FIG. 3, at the end of a direction passing through themolecule passage opening of the valve seat 45, which can beopened/closed by means of the valve 43, there is provided the moleculeradiation portion 21. This molecule radiation portion 21 has acylinder-like molecule heater chamber 22, and surrounding this moleculeheater chamber 22 is provided the heater 25. Molecules of the thin-filmelement-forming material, leaking from the side of the valve 43mentioned above and reaching the molecule radiation portion 21 areheated again (i.e., re-heated), up to the desired temperature withinthis molecule heater chamber 22, and are irradiated from the moleculedischarge openings 24 towards the substrate.

According to the present invention, controls are made upon theservomotors 36 and 46, which adjust the opening of the valves 33 and 43through driving them. At the same time, control is also made on anelectric power source, which supplies electric power to the heaters 32and 42 for heating the crucibles 31 and 41. Those controls are conductedwith a programming control, through feed-back of the volumes of themolecular beams discharged from the molecular beam source cells 1 and 2,which are detected by the film-thickness meters 16 and 26 and, also,information relating to the openings of the valves 33 and 43, which areopened by the servomotors 36 and 46.

FIG. 5 is a view for showing a flow sheet of that control system.Basically, the same control system is applied to both of the molecularbeam source cells 1 and 2 and the elements of the control system for themolecular beam source cell 2 are indicated by the reference numerals inparentheses.

As is shown in this FIG. 5, signals are generated from thefilm-thickness meters 16 and 26, depending upon the volumes of themolecular beams discharged from the molecular beam source cells 1 and 2,and those signals are transmitted from processors 17 and 27 to valvecontrollers 37 and 47 and heater controllers 38 and 48, throughmolecular beam controllers 18 and 28, respectively.

In an initial period of the operation thereof, the molecular beamcontroller 18 or 28 transmits an instruction value relating totemperature of the crucible 31 or 41, which is determined in advance, tothe heater controller 38 or 48 serving also as an electric power sourcethereof and, at the same time, calculates an opening instruction valuefor the valve from a preset target value of the volume of the molecularbeam and information relating to the present value of the volume of themolecular beam, which is transmitted from the film-thickness meter 16 or26 through the processor 17 or 27, so as to send it to the valvecontroller 37 or 47.

The valve controller 37 or 47 transmits a driving signal to theservomotor 36 or 46 of the valve 33 or 43 on the basis of the openinginstruction value, which is transmitted from the processor 17 or 27, andthereby adjusts the opening of the valve 33 or 43, i.e., the ratio (i)of the cross-sectional area of the flow passage of the valve 33 or 34 tothat when it is fully opened. Together with this, it also transmits theopening of the valve 33 or 34 to the molecular beam controller 18 or 28.

As a matter of course, when the volume of the molecular beam, which isdetected by the film-thickness meter 16 or 26, does not reach a targetthereof, the molecular beam controller 18 or 28 makes an adjustment tothe valve opening instruction value, in such a manner or direction thatthe opening of the valve 33 or 34 becomes larger, while when the volumeof the molecular beam exceeds the target, the valve opening instructionvalue is adjusted so that the opening of the valve 33 or 34 becomessmaller, in the direction thereof.

On the other hand, the heater controller 38 or 48 controls the electricpower to be supplied to the heater 32 or 42, so that the temperature ofthe crucible 31 or 41 measured by the thermocouple, etc., maintains theinstruction value, which is provided from the molecular beam controller18 or 28. Herein, when the present value of the opening of the valve 33or 43 exceeds an upper limit value thereof, which is determined inadvance, the molecular beam controller 18 or 28 transmits theinstruction value signal to the heater controller 38 or 48, so as toincrease the temperature of the crucible 31 or 41. When the temperatureof the crucible 31 or 41 increases, since the vapor pressure of thethin-film element-forming material “a” or “b” within the crucible 31 or41 increases, then the volume of molecular beam increases, even at thesame opening of that valve. For this reason, the molecular beamcontroller 18 or 28 decreases the valve opening instruction valuetransmitted to the valve controller 37 or 47, trying to maintain thevolume of the molecular beam to be constant and, therefore, as a resultthereof, the present value of the opening of the valve 33 or 43 is socontrolled that it comes to be lower than the upper limit value. Also, aregion of increasing temperature is controlled so that the temperaturecan rise up to a temperature increasing value, which is determined inadvance, or the opening of the valve 33 or 43 is controlled so that itcomes to be lower than that, which is determined in advance.

Contrarily, when the present value of opening of the valve 33 or 43 islower than a lower limit value thereof, which is determined in advance,the molecular beam controller 18 or 28 transmits an instruction valuesignal to the heater controller 38 or 48, so as to decrease thetemperature of the crucible 31 or 41, thereby lowering the temperatureof the crucible 31 or 41.

When an indicated value of opening of the valve 33 or 43 of theservomotor 36 or 46 lies between the upper limit value and the lowerlimit value, which are determined in advance, no change is made to theinstructions to the heater controller 38 or 48.

FIG. 6 shows the time diagram of the controls mentioned above. Whenbecoming small in the amount or volume of the thin-film element-formingmaterial “a” or “b” within the crucible 31 or 41, accompanying theconsumption thereof, then the value of the evaporation of the thin-filmelement-forming material “a” or “b” within the crucible 31 or 41 isdecreased, gradually. The molecular beam, which is discharged from themolecule discharge opening 14 or 24 of the molecular beam source cell 1or 2, is controlled to be constant in the volume thereof, responding tothis by means of the molecular beam controller 18 or 28, therefore, theopening of the valve 33 or 43 becomes larger with the elapse of time.When the opening of the valve 33 or 43 exceeds the upper limit value“U”, which is determined in advance, a temperature increase instructionis given from the molecular beam controller 18 or 28 to the heatercontroller 38 or 48, so that the crucible 31 or 41 increases thetemperature thereof. Accompanying this, the volume of the molecularbeam, which is detected by the film-thickness meter 16 or 26 per hour,increases in the tendency thereof. For maintaining the volume of themolecular beam, which is discharged from the molecule discharge opening14 or 24 of the molecular beam source cell 1 or 2, to be constant,responding to this, the servomotor 36 or 46 of the valve 33 or 43 isdriven by means of the valve controller 37 or 47, i.e., the opening ofthe valve 33 or 43 is controlled to decrease. Thereafter, when thevolume of the molecular beam, which is detected by the film-thicknessmeter 16 or 26 per hour, changes the tendency thereof to increase, thenfor maintaining the volume of the molecular beam discharged from themolecule discharge opening 14 or 24 of the molecular beam source cell 1or 2 constant, the opening of the valve 33 or 43 is controlled to belarger by the valve controller 37 or 47, again. In this manner, thevolume of the molecular beam, which is detected by the film-thicknessmeter 16 or 26 per hour, is controlled to be constant, i.e. maintaininga stable value thereof.

However, when increasing the temperature of the crucible 31 or 41 in astep-like manner by a unit or width of temperature increase which isdetermined in advance, that unit or width of temperature increase mustbe determined in advance through experimentation and/or calculation atthe temperature that the volume of the molecular beam, which is detectedby the film-thickness meter 16 or 26 per hour, changes the tendencythereof to decrease under the condition where the opening of the valve33 or 43 does not reach the lower limit value “L”, and then there is thenecessity of increasing the valve opening thereafter.

Although the embodiment mentioned above shows the example of obtainingthe film forming through the discharge of the molecular beams from thetwo (2) molecular beam source cells towards the substrate 51, however,it is of course that the present invention can also be applied to a casewhere the film forming is obtained through the discharge of themolecular beam from a single molecular beam source cell towards thesubstrate 51, or into a case where the film forming is obtained throughdischarge of the molecular beams from three (3) or more of the molecularbeam source cells towards the substrate 51, and so on.

The present invention may be embodied in other specific forms withoutdeparting from the spirit, essential features or characteristicsthereof. The present embodiment(s) is/are therefore to be considered inall respects as illustrative and not restrictive, the scope of theinvention being indicated by the appended claims rather than by theforgoing description and the range of equivalency of the claims aretherefore to be embraced therein.

1. A method for controlling the volume of a molecular beam used informing a thin film on a substrate, comprising the steps of: providing acrucible containing a thin-film element-forming material; heating saidcrucible with a heater to generate molecules of the thin-filmelement-forming material; discharging the molecules of the thin-filmelement-forming material from the crucible through a molecule dischargepassage towards a film-forming surface of the substrate; providing avacuum container having a hermetically sealed structure for receivingthe crucible, the heater and the molecule discharge passage therein;adjusting the volume of the molecules of the thin-film element-formingmaterial discharged from the crucible by a first valve provided at themolecule discharge passage; detecting the volume of the molecules of thethin-film element-forming material directed towards the film-formingsurface; providing a first controller means configured to adjust theopening of the first valve based on feed-back information of thedetected volume of the molecules of the thin-film element-formingmaterial; providing an electric power source for supplying electricpower to the heater; providing a second controller means configured toadjust the electric power supplied to the heater based on the feed-backinformation of the detected volume of the molecules of the thin-filmelement-forming material and first valve opening information; andadjusting the electric power supplied to the heater when a valuecorresponding to the opening of the first valve exceeds a predeterminedupper limit or is less than a predetermined lower limit.
 2. The methodof claim 1, additionally comprising the steps of: providing a secondcrucible containing a second thin-film element-forming material; heatingsaid second crucible with a second heater to generate molecules of thesecond thin-film element-forming material; discharging the molecules ofthe second thin-film element-forming material from the second cruciblethrough a second molecule discharge passage towards the film-formingsurface of the substrate; providing the second crucible, the secondheater and the second molecule discharge passage in the hermeticallysealed structure; adjusting the volume of the molecules of the secondthin-film element-forming material discharged from the second crucibleby a second valve provided at the second molecule discharge passage;detecting the volume of the molecules of the second thin-filmelement-forming material directed towards the film-forming surface;providing a third controller means configured to adjust the opening ofthe second valve based on the feed-back information of the detectedvolume of the molecules of the second thin-film element-formingmaterial; providing a second electric power source for supplyingelectric power to the second heater; providing a fourth controller meansconfigured to adjust the electric power supplied to the second heaterbased on the feed-back information of the detected volume of themolecules of the second thin-film element-forming material and secondvalve opening information; and adjusting the electric power supplied tothe second heater when a value corresponding to the opening of thesecond valve exceeds a predetermined upper limit or is less than apredetermined lower limit.
 3. The method of claim 1, wherein the volumeof the molecules of the thin-film element-forming material is detectedby a film-thickness meter.
 4. The method of claim 2, wherein the volumeof the molecules of the second thin-film element-forming material isdetected by a film thickness meter.